OSU to study diseases affecting common nursery plants

CORVALLIS, Ore. – Oregon State University plans to use a $3 million grant to study two groups of bacteria that result in millions of dollars in losses annually to the nation’s nursery industry.

Researchers will study Agrobacterium tumefaciens and Rhodococcus fascians, which deform hundreds of common landscape plants, including hostas, Shasta daisies, petunias and pansies.

These bacterial pathogens are of particular concern in Oregon, where the greenhouse and nursery industry contributes more than $745 million to the Oregon economy annually. Some growers report losses of up to $100,000 a year to gall-forming bacterial diseases.

The four-year grant, from the USDA's National Institute of Food and Agriculture, will help determine how these pathogens are introduced into nurseries and how they establish and persist; develop new approaches to improve detection and control; and help nursery workers recognize and prevent the spread of the pathogens.

For more than a decade Melodie Putnam, chief diagnostician at OSU's Plant Clinic, has been working with Oregon nurseries to correctly identify these bacterial pathogens that are responsible for tumor-like galls and cancer-like leaf growth in infected plants. Correct identification of the bacterial pathogen is a necessary first step to preventing disease, Putnam said.

“It is difficult to combat a problem if you don’t recognize it for what it is,” she said.

These two types of bacteria have “wily life histories that help them evade detection,” Putnam added. R. fascians can grow on the surface of plants without causing any symptoms for months before moving into plant tissue and triggering a proliferation of leafy galls, deforming the plant and making it unmarketable. The ubiquitous R. fascians has been found in environments such as cheese rinds, glacial ice cores, the stomach of Atlantic hagfish and the backs of fly-bitten sheep.

A. tumefaciens infects plants by injecting and integrating a portion of its DNA into the genome of the host plant. Scientists have long used non-pathogenic variants of A. tumefaciens in the process of plant genetic engineering. Using the bacteria's natural infection process, it is possible to genetically modify plants to express novel traits such as increased synthesis of vitamin A in rice to combat nutrient deficiencies.

Long before its remarkable biology was fully understood, A. tumefaciens was known to cause crown gall disease, which alters plant metabolism and swells tissues into tumors, called galls.

“A. tumefaciens has caused up to 40 percent reductions in yield in some perennial crops, and as much as 100 percent loss in roses,” Putnam said.

Despite the obvious disease symptoms, both of these pathogens can be easily misdiagnosed, Putnam said, which slows the response to a spreading infection.

“Unfortunately, there is no treatment for either A. tumefaciens or R. fascians at this time," she said. "Therefore, steps must be taken to prevent disease.”

The project will be carried out by an interdisciplinary team that will include the following:

Jeff Chang, a molecular plant pathologist in OSU’s College of Agricultural Sciences, will lead the team.

Niklaus Grunwald, a plant pathologist with the U.S. Department of Agriculture, will use genomic epidemiology to understand where the pathogens hide, move and change over time.

Melodie Putnam, the chief diagnostician at OSU's Plant Clinic, will use whole genome sequences to design more effective diagnostic methods for rapid detection and identification.

Taifo Mahmud, a natural product chemist in OSU’s College of Pharmacy, will aim to develop less toxic control compounds and will work with Putnam to develop safe practices for chemical control.

Luisa Santamaria, a nursery specialist with the OSU Extension Service, plans to develop information in Spanish and English to help nursery workers prevent the spread of bacterial diseases in the field and greenhouses.

Clark Seavert, an economist with OSU Extension, will assess the economic benefits to the industry of this research and workforce education.

Story Source

Jeff Chang

Rhodococcus fascians creates many small, short shoots on common plants such as Shasta daisy.

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